Hearts, both physical and metaphorical, are a constant symbol throughout the novel. This idea is best represented in the complementary yet dichotomous characters of Reese and Emma:

If my wonderings about life were scientific, bent toward examination and physical discovery, Emma’s all leaned toward matters of the heart. While I could understand and explain the physics behind a rainbow, Emma saw the colors (48).

While Reese views the heart from a medical perspective, Emma viewed it as an instrument of love. He sees the heart’s physical function as a miracle; Emma prioritized the heart’s ability to love. For much of the novel, when Reese considers the heart, he thinks about it as a surgeon would. He learned about the anatomy of the human heart: He read textbooks, went to medical school, and became a surgeon, all in the hopes of one day fixing Emma’s heart. From Emma’s perspective, Reese has given her his heart; her heart is saved more by his love than by his surgical prowess. When Emma died, Reese felt like a failure because he couldn’t save her physical heart, but by the end of the novel he comes to realize that his love for her mattered more.